linux-kernel - Re: [PATCH] mm: Add new vma flag VM_LOCAL

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Date:   Tue, 22 May 2018 10:03:54 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Christopher Lameter <cl@...ux.com>
Cc:     Boaz Harrosh <boazh@...app.com>, Jeff Moyer <jmoyer@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Rik van Riel <riel@...hat.com>, Jan Kara <jack@...e.cz>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Amit Golander <Amit.Golander@...app.com>
Subject: Re: [PATCH] mm: Add new vma flag VM_LOCAL_CPU

On 05/22/2018 09:46 AM, Christopher Lameter wrote:
> On Tue, 22 May 2018, Dave Hansen wrote:
> 
>> On 05/22/2018 09:05 AM, Boaz Harrosh wrote:
>>> How can we implement "Private memory"?
>> Per-cpu page tables would do it.
> We already have that for percpu subsystem. See alloc_percpu()

I actually mean a set of page tables which is only ever installed on a
single CPU.  The CPU is architecturally allowed to go load any PTE in
the page tables into the TLB any time it feels like.  The only way to
keep a PTE from getting into the TLB is not ensure that a CPU never has
any access to it, and the only way to do that is to make sure that no
set of page tables it ever loads into CR3 have that PTE.

As Peter said, it's possible, but not pretty.